1. Field of the Invention
The present invention relates to a satellite signal receiving antenna apparatus for receiving radio wave from an artificial satellite, particularly relates to a satellite signal receiving antenna apparatus for receiving circularly polarized radio wave as in satellite radio broadcast.
2. Description of the Related Art
Conventionally, as an antenna for receiving radio wave from an artificial satellite, for example, a GPS receiving antenna for receiving radio wave from a GPS (Global Positioning System) satellite is known and a so-to-speak patch antenna is used therefor. A patch antenna is provided with a grounding electrode formed by a conductive material on one principal face of a ceramic board constituting an insulating member and provided with a receiving electrode at other principal face of the ceramic board for outputting a received signal to an outside circuit by a feeding pin.
In contrast thereto, in recent years, there has been promoted to provide radio broadcast or the like by circularly polarized radio wave transmitted from an artificial satellite and when such a radio broadcast is received, a so-to-speak satellite radio broadcast receiving antenna is used (refer to, for example, JP-A-2003-78343).
As shown by FIG. 6, a satellite radio broadcast receiving antenna is provided with a first metal plate 21 as a grounding electrode, a second metal plate 22 constituted by being arranged to be opposed to the first metal plate 21 to separate therefrom by a predetermined interval, and a pair of inverse-F shape antennas 23 arranged to dispose in a space constituted between the first metal plate 21 and the second metal plate 22.
The first metal plate 21 is formed in a shape of a rectangular flat plate by a metal material and attached to a lower cover 24. Further, the second metal plate 22 is formed by a metal material and attached to an upper cover 25. Further, there is constituted a structure of containing the respective portions at an inner space of a cover portion 26 constituted by the lower cover 24 and the upper cover 25.
Further, the inverse-F shape antenna 23 is formed in a wire-like shape by a material having conductivity of, for example, a metal or the like and is supported by an attaching member 28 formed by, for example, a resin material or the like above a principal face of the first metal plate 21 in a state of being separated from the first metal plate 21.
Meanwhile, the above-described satellite radio broadcast receiving antenna is arranged with the pair of inverse-F shape antennas 23 such that antenna portions thereof in a wire-like shape extended horizontally are orthogonal to each other in order to achieve an excellent receiving characteristic with regard to, for example, left and right circularly polarized radio waves. The pair of inverse-F shape antennas 23 are attached with the antenna portions in the wire-like shape symmetrically with each other and therefore, in assembling, two kinds of the inverse-F shape antennas 23 symmetrical with each other are needed.
In a prior art, according to the inverse-F shape antenna 23, as shown by, for example, FIG. 7, the antenna portion 31 in the wire-like shape and the attaching member 28 made of a plastic are integrally molded by insert molding, however, when the insert molding is adopted, an increase in cost is brought about. Particularly, when there are prepared two kinds of the inverse-F shape antennas 23 symmetrical with each other are prepared in correspondence with left and right circularly polarized radio waves, two kinds of insert molding dies or the like are needed in correspondence with the respective shapes to bring about a further increase in fabrication cost.